With the discovery of living cationic polymerization, the synthesis of polyisobutylenes (PIBs) with controlled molecular weight and quantitative end functionality was made possible. Today, it is known that allyl-terminated (.about.CH.sub.2 C(CH.sub.3).sub.2 --CH.sub.2 CH.dbd.CH.sub.2) polyisobutylenes can be quantitatively endlinked by hydrosilation with molecules containing an SiH moiety. This reaction results in the formation of a hydrolytically stable Si-C bond. Heretofore, however, research into the usefulness of the quantitative end functionality of polyisobutylene and the ability of allyl-terminated PIBs to be endlinked via hydrosilation with siloxane compounds has centered on the production of star polymers and star block copolymers. For instance, U.S. Pat. No. 5,663,245 teaches the synthesis and characterization of multi-arm star polymers comprising polyisobutylene arms emanating from a well-defined siloxane core. Star block copolymers have been produced using polyisobutylene-b-polystyrene arms emanating from a well-defined siloxane core. There has been little, if any, study into the usefulness of this synthesis reaction in the production of networks such as bicomponent networks or multi-block copolymers.
The polymeric networks of the present invention, and particularly bicomponent networks (BCNs), should be distinguished from more traditional interpenetrating polymer networks (IPNs). A BCN is defined as a single elastomeric network comprising two chemically different covalently bonded sequences; whereas, an IPN consists of two or more unlinked independent networks. The distinction to be made is significant in that the polymers in the IPNs are not linked chemically, but rather are two separate networks tangled within one another. Most two-component systems studied to date concern IPNs, with very few studies having been performed using BCNs. The distinction between BCNs and IPNs is more particularly set forth schematically hereinbelow. ##STR1##
It will be appreciated that multiblock copolymers are like BCNs in that they also comprise two chemically different covalently bonded sequences, but are not crosslinked in the manner that BCNs are crosslinked. Rather, multiblock copolymers are linear blocks of at least two polymers, such as, for the present invention, polyisobutylene (-A-) and any of a number of difunctional linear polysiloxanes (-B-), endlinked together to form multiple block copolymers (-A-B-)n. Notably, these block copolymers are synthesized differently from "regular" block copolymers in that the polymers (-A-) and (-B-) are already formed before endlinking takes place. However, they are not "bicomponent networks" either, as defined hereinabove, because they are not crosslinked and, therefore, are not elastomeric in nature and are soluble in various solvents.
BCNs traditionally have required that the two crosslinked components at least contribute theoretically to the physical and chemical characteristics of the polymeric networks. That is, the properties of the bicomponent network will reflect those of the individual components. For example, bicomponent networks containing polyisobutylenes and polysiloxanes may be of great interest to the extent that polyisobutylene is known for low cost, superior mechanical properties, extremely low gas permeability and excellent environmental, hydrolytic and high temperature resistance while, in contrast, siloxanes are relatively expensive, have poor mechanical properties, but excel in regard to high gas permeability, low surface energy and bicompatibility. Thus, it is believed that elastomeric BCNs with varying ratios of polyisobutylene to polysiloxane such as polydimethylsiloxane (PDMS) may be of use to control gas permeability, water repellency, environmental stability and bicompatibility.
It will be appreciated that polymeric networks may also be formed from two components, but the second component may be used in such small and insignificant amounts that the second component would not contribute to the physical and chemical characteristics of the polymeric network. In this instance, the network is not considered a "bicomponent network" as defined hereinabove, inasmuch as the properties of the network are essentially the same as the properties of the primary (first) component.
These polymeric networks, including particularly, BCNs and other networks containing polyisobutylene of known structure, and especially those with desirable or known number average molecular weights between crosslinks (Mc) and easily obtainable crosslinking functionalities, may be very useful for the study of rubber elasticity theories and for the possible extension of these theories to two-component systems, since the polyisobutylene prepolymers and siloxanes are well-defined and can easily be characterized prior to crosslinking.